NCERT Exemplar Problems for Class 10 Science

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Chapter 16: Management of Natural Resources

Quick Revision:

Chapter 1: Chemical Reactions and Equations

A complete chemical equation represents the reactants, products and their physical states symbolically.

A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.

In a combination reaction two or more substances combine to form a new single substance.

Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.

Reactions in which heat is given out along with the products are called exothermic reactions.

Reactions in which energy is absorbed are known as endothermic reactions.

When an element displaces another element from its compound, a displacement reaction occurs.

Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.

Precipitation reactions produce insoluble salts.

Reactions also involve the gain or loss of oxygen or hydrogen by substances.

Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.

Chapter 2: Acids, Bases and Salts

Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases.

Acidic nature of a substance is due to the formation of H+(aq) ions in solution. Formation of OH–(aq) ions in solution is responsible for the basic nature of a substance.

When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.

When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen.

When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives the corresponding salt, carbon dioxide gas and water.

Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.

The strength of an acid or an alkali can be tested by using a scale called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution.

A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution a pH more than 7.

Living beings carry out their metabolic activities within an optimal pH range.

Mixing concentrated acids or bases with water is a highly exothermic process.

Acids and bases neutralise each other to form corresponding salts and water.

Water of crystallisation is the fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form.

Salts have various uses in everyday life and in industries.

Chapter 3: Metals and Non – Metals

Elements can be classified as metals and non-metals.

Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid.

Metals can form positive ions by losing electrons to non-metals.

Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known as amphoteric oxides.

Different metals have different reactivities with water and dilute acids.

A list of common metals arranged in order of their decreasing reactivity is known as an activity series.

Metals above hydrogen in the Activity series can displace hydrogen from dilute acids.

A more reactive metal displaces a less reactive metal from its salt solution.

Metals occur in nature as free elements or in the form of their compounds.

The extraction of metals from their ores and then refining them for use is known as metallurgy.

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion.

Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.

Non-metals form negatively charged ions by gaining electrons when reacting with metals.

Non-metals formoxides which are either acidic or neutral.

Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides.

Chapter 4: Carbon and its Compounds

Chapter 5: Periodic Classification of Elements

Chapter 6: Life Processes

Movement of various types can be taken as an indication of life.

The maintenance of life requires processes like nutrition, respiration, transport of materials within the body and excretion of waste products.

Autotrophic nutrition involves the intake of simple inorganic materials from the environment and using an external energy source like the Sun to synthesise complex high-energy organic material.

Heterotrophic nutrition involves the intake of complex material prepared by other organisms.

In human beings, the food eaten is broken down by various steps along the alimentary canal and the digested food is absorbed in the small intestine to be sent to all cells in the body.

During the process of respiration, complex organic compounds such as glucose are broken down to provide energy in the form of ATP. ATP is used to provide energy for other reactions in the cell.

Respiration may be aerobic or anaerobic. Aerobic respiration makes more energy available to the organism.

In human beings, the transport of materials such as oxygen, carbon dioxide, food and excretory products is a function of the circulatory system. The circulatory system consists of the heart, blood and blood vessels.

In highly differentiated plants, transport of water, minerals, food and other materials is a function of the vascular tissue which consists of xylem and phloem.

In human beings, excretory products in the form of soluble nitrogen compounds are removed by the nephrons in the kidneys.

Plants use a variety of techniques to get rid of waste material. For example, waste material may be stored in the cell-vacuoles or as gum and resin, removed in the falling leaves, or excreted into the surrounding soil.

Chapter 7: Control and Coordination

Control and coordination are the functions of the nervous system and hormones in our bodies.

The responses of the nervous system can be classified as reflex action, voluntary action or involuntary action.

The nervous system uses electrical impulses to transmit messages.

The nervous system gets information from our sense organs and acts through our muscles.

Chemical coordination is seen in both plants and animals.

Hormones produced in one part of an organism move to another part to achieve the desired effect.

A feedback mechanism regulates the action of the hormones.

Chapter 8: How do Organisms Reproduce?

Chapter 9: Heredity and Evolution

Chapter 10: Light – Reflection and Refraction

Chapter 11: Human Eye and Colourful World

Chapter 12: Electricity

A stream of electrons moving through a conductor constitutes an electric current. Conventionally, the direction of current is taken opposite to the direction of flow of electrons.

The SI unit of electric current is ampere.

To set the electrons in motion in an electric circuit, we use a cell or abattery. A cell generates a potential difference across its terminals. It is measured in volts (V).

Resistance is a property that resists the flow of electrons in a conductor. It controls the magnitude of the current. The SI unit of resistance is ohm (Ω).

Ohm’s law: The potential difference across the ends of a resistor is directly proportional to the current through it, provided its temperature remains the same.

The resistance of a conductor depends directly on its length, inversely on its area of cross-section, and also on the material of the conductor.

The equivalent resistance of several resistors in seriesis equal to the sum of their individual resistances.

A set of resistors connected in parallel has an equivalent resistance Rp given by 1/Rp = 1/R1 + 1/R2 + 1/R3.

The electrical energy dissipated in a resistor is given by W = V × I × t

The unit of power is watt (W). One watt of power is consumed when 1 A of current flows at a potential difference of 1 V.

Chapter 13: Magnetic Effects of Electric Current

A compass needle is a small magnet. Its one end, which points towards north, is called a north pole, and the other end, which points towards south, is called a south pole.

A magnetic field exists in the region surrounding a magnet, in which the force of the magnet can be detected.

Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take. Field lines are shown closer together where the magnetic field is greater.

A metallic wire carrying an electric current has associated with it a magnetic field. The field lines about the wire consist of a series of concentric circles whose direction is given by the right-hand rule.

The pattern of the magnetic field around a conductor due to an electric current flowing through it depends on the shape of the conductor. The magnetic field of a solenoid carrying a current is similar to that of a bar magnet.

An electromagnet consists of a core of soft iron wrapped around with a coil of insulated copper wire.

A current-carrying conductor when placed in a magnetic field experiences a force. If the direction of the field and that of the current are mutually perpendicular to each other, then the force acting on the conductor will be perpendicular to both and will be given by Fleming’s left-hand rule. This is the basis of an electric motor. An electric motor is a device that converts electric energy into mechanical energy.

The phenomenon of electromagnetic induction is the production of induced current in a coil placed in a region where the magnetic field changes with time. The magnetic field may change due to a relative motion between the coil and a magnet placed near to the coil. If the coil is placed near to a current-carrying conductor, the magnetic field may change either due to a change in the current through the conductor or due to the relative motion between the coil and conductor. The direction of the induced current is given by the Fleming’s right-hand rule.

A generator converts mechanical energy into electrical energy. It works on the basis of electromagnetic induction.

In our houses we receive AC electric power of 220 V with a frequency of 50 Hz. One of the wires in this supply is with red insulation, called live wire. The other one is of black insulation, which is a neutral wire. The potential difference between the two is 220 V. The third is the earth wire that has green insulation and this is connected to a metallic body deep inside earth. It is used as a safety measure to ensure that any leakage of current to a metallic body does not give any severe shock to a user.

Fuse is the most important safety device, used for protecting the circuits due to short-circuiting or overloading of the circuits.